Toward Perfection: Kapellasite, Cu3Zn(OH)6Cl2, a New Model S = 1/2 Kagome Antiferromagnet

The search for the resonating valence bond (RVB) state continues to underpin many areas of condensed matter research. The RVB is made from the dimerisation of spins on different sites into fluctuating singlets, and was proposed by Anderson to be the reference state from which the transition to BCS superconductivity occurs. Little is known about the state experimentally, due to the scarcity of model materials. Theoretical work has put forward the S = 1/2 kagome antiferromagnet (KAFM) as a good candidate for the realization of the RVB state. In this paper we introduce a new model system, the S = 1/2 KAFM Kapellasite, Cu3Zn(OH)6Cl2. We show that its crystal structure is a good approximation to a 2-dimensional kagome antiferromagnet and that susceptibility data indicate a collapse of the magnetic moment below T = 25 K that is compatible with the spins condensing into the non-magnetic RVB state.Comment: Communication, 3 pages, 3 figure

Hydrothermal Synthesis of Delafossite-Type Oxides

The syntheses of copper and silver delafossite-type oxides from their constituent binary metal oxides, oxide hydroxides and hydroxides, by low temperature (<210 °C) and low pressure (<20 atm) hydrothermal reactions are described. Particular emphasis is placed on how the acid-base character of a constituent oxide determines its solubility and therefore whether a particular delafossite-type oxide can be synthesized, a strategy utilized by geologists and mineralogists to understand the conditions necessary for the synthesis of various minerals. Thus, the geochemical and corrosion science literature are shown to be useful in understanding the reaction conditions required for the syntheses of delafossite-type oxides and the relationship between reactant metal oxide acid-base character, solubility, aqueous speciation, and product formation. Manipulation of the key parameters, temperature, pressure, pH, and reactant solubility, results in broad families of phase-pure delafossite-type oxides in moderate to high yields for copper, CuBO2 (B) Al, Sc, Cr, Mn, Fe, Co, Ga, and Rh), and silver, AgBO2 (B ) Al, Sc, Fe, Co, Ni, Ga, Rh, In, and Tl)

Ultra-Light Amorphous Silicon Cell for Space Applications

For space applications, solar cells should be optimized for highest power density rather than for highest efficiency. In this context, relatively low efficiency thin-film solar cell may well surpass multi-junction III-V based solar cells if they can be made thin enough. In thin-film solar cells the power density is mostly limited by the substrate. The introduction of ultra-thin polymeric substrates is the key for decreasing the cell mass. In this work, a very thin polyimide film LaRCtrade-CP1 was used as substrate or superstrate for amorphous silicon solar cell fabrication. CP1 films were either fixed on a glass carrier or spin coated onto a glass carrier coated with a release agent. By depositing amorphous silicon cells on 6 mum thick CP1 films, a power density of 2.9 W/g under AM1.5g and of 3.9 W/g (estimated) under AM0 illumination spectra was achieved, in substrate (n-i-p) configuration (for a cell area of ca. 0.25 cm2). A similar cell deposited in superstate (p-i-n) configuration exhibits a record power density of 3.2 W/g under AM1.5g and an estimated value of 4.3 W/g under AM0 illumination spectra. Release of the finished solar cells from the glass carrier was also tested

Hole Mobility in µc-Si:H

In microcrystalline hydrogenated silicon (μc-Si:H), the drift mobility dependencies of holes on electric field and temperature have been measured by using a method of equilibrium charge extraction by linearly increasing voltage. At room temperature the estimated value of the drift mobility of holes is much lower than in crystalline silicon and slightly higher than in amorphous hydrogenated silicon (a-Si:H). In the case of stochastic transport of charge carriers with energetically distributed localized states, the numerical model of this method gives insight into the mobility dependence on electric field. From the numerical modeling and experimental measurement results, it follows that the hole drift mobility dependence on electric field is predetermined by electric field stimulated release from localized states. © 2001 American Institute of Physics